In the conventional preparation of a metal substrate comprising a catalyst coating layer, the representative catalyst coating methods were an impregnation method, wherein the metal substrate is impregnated in a catalyst precursor solution to support the catalyst, and a washing coating method, wherein the metal surface is coated with a catalyst using a slurry solution which is a mixture of a powder catalyst, whose catalyst is supported by a carrier in advance, and an alumina sol.
In achieving a certain amount of catalyst loading, the impregnation method has the problems of increase of number of impregnation and difficult control of dispersion of the active metal particles due to the low catalyst loading amount. Also, the washing coating has the problem of the weak binding strength between the catalyst coating layer and the metal substrate since controlling coating layer thickness and uniform coating are difficult. Furthermore, it needs a large amount of catalyst due to the much loss of coating solution.
Thus, the present inventors had developed a method for preparing a metal structured catalyst, which comprises contacting a mixed solution including a precursor of the metal catalyst and a precipitating agent with the metal substrate to form a metal precipitate on the metal substrate and performing heat treatment, whereby metal nanoparticles were supported more uniformly and with high dispersion and the binding strength between the catalyst layer and the metal substrate surface was enhanced (Korean Patent No. 10-1403698).
However, when a precursor of a ruthenium catalyst was applied to the above method to form a ruthenium catalyst layer, the coating layer of the ruthenium catalyst was not formed well on the metal substrate surface. Thus, according to the above method, it was not easy to form a ruthenium catalyst layer exhibiting appropriate catalytic activity.